The present invention relates to novel pyrrylfluoran compounds which are colorless or essentially colorless, but are instantaneously colorable when brought into reactive contact with suitably sensitized sheets containing an acidic electron-acceptor such as the protic acids, e.g., organic acids, phenolic acids, phenols, diphenols, phenolic resins of the novolak type, and aprotic acids, e.g., Lewis acids, acid clays, etc., or mixtures of these materials. These properties and others disclosed hereinafter make the compounds of this invention suitable for use in various types of carbonless pressuresensitive copy papers, thermally-sensitive imaging papers, thermally-sensitive imaging transparencies for overhead projection screens and other copy or image applications.
A number of chemical compounds are disclosed in the prior art to be useful as color-precursors when brought into contact with acidic electron-acceptors. Included in the suitable compounds are the 2-amino-6-dialkylaminofluoran compounds the preparation of which and/or use in pressure sensitive papers are disclosed in U.S. Pat. Nos. 3,501,331; 3,624,107; 3,824,119; 3,825,561; and 3,839,361. Belgian Pat. No. 795,747 discloses 2-amino-6-dialkylaminofluoran compounds in which the 2-amino group is part of a fully reduced 5 or 6 membered heterocyclic ring such as pyrrolidine, piperidine, piperazine, morpholine and thiomorpholine.